An oscillator circuit comprises a crystal oscillator arranged to generate an oscillation signal, a bias current generator arranged to supply a bias current to the crystal oscillator, and a feedback stage arranged to generate a feedback signal in response to an amplitude of the oscillation signal reaching an amplitude threshold. The bias current generator is arranged to: in response to a supply of power to the oscillator circuit being switched on, generate the bias current at an increasing level commencing from a first level; in response to the feedback signal, terminate the increasing; and during subsequent oscillation of the crystal oscillator, supply the bias current at a second level dependent on a final level of the bias current reached when the increasing is terminated.

An oscillator circuit comprises a crystal oscillator and an inverter. The input of the inverter is connected to the first terminal of the crystal oscillator and the output of the inverter is connected to the second terminal of the crystal oscillator, oscillator circuit is arranged to operate the inverter in its linear operating region. An amplitude regulator has an input connected to the input of the inverter, arranged to provide a first supply current I.sub.AREG to the inverter, where the magnitude of the first supply current is inversely dependent on a magnitude of a voltage at the inverter input. A digital-to-analogue converter is arranged to provide a second supply current I.sub.DAC to the inverter having a magnitude determined by a digital signal applied to a digital input of the digital-to-analogue converter.

A voltage controlled oscillator includes a resonator and an amplifier. The resonator includes a capacitive element and an inductive element. The inductive element has a plurality of conductive segments forming a physical loop. The inductive element has electrical connections on the physical loop to the plurality of conductive segments forming at least one electrical loop disposed within an interior space formed by the physical loop. The amplifier has an input and an output, the input coupled to a first conductive segment forming a first impedance and the output coupled to a second conductive segment forming a second impedance.

An integrated circuit includes an inverter, first and second capacitors, a resistor, and a transistor. The inverter has an input and an output. The first capacitor is coupled to a ground. The transistor has a first transistor terminal, a second transistor terminal, and a control input. The first transistor terminal is coupled to the first capacitor and the second transistor terminal is coupled to the input of the inverter. The second capacitor is coupled between the output of the inverter and the ground. The resistor is coupled between the output of the inverter and the first transistor terminal.

An integrated circuit includes an inverter, first and second capacitors, a resistor, and a transistor. The inverter has an input and an output. The first capacitor is coupled to a ground. The transistor has a first transistor terminal, a second transistor terminal, and a control input. The first transistor terminal is coupled to the first capacitor and the second transistor terminal is coupled to the input of the inverter. The second capacitor is coupled between the output of the inverter and the ground. The resistor is coupled between the output of the inverter and the first transistor terminal.

An oscillation circuit includes an oscillator (X.sub.1), capacitors (C.sub.1, C.sub.2) connected between two terminals of the oscillator (X.sub.1), and an amplification circuit (A.sub.1) having an input terminal connected to a connecting point between the oscillator (X.sub.1) and the capacitor (C.sub.1) and an output terminal connected to a connecting point between the capacitor (C.sub.1) and the capacitor (C.sub.2). The amplification circuit (A.sub.1) includes an n-type transistor (M.sub.1) and a p-type transistor (M.sub.2) respectively having source terminals, the connecting point of which is connected to the output terminal of the amplification circuit (A.sub.1), a p-type transistor (M.sub.3) configured to connect a gate terminal of the n-type transistor (M.sub.1) to a power supply terminal at the time of an oscillation stop and disconnect the power supply terminal and the gate terminal of the n-type transistor (M.sub.1) at the time of an oscillation operation, and an n-type transistor (M.sub.4) configured to connect a gate terminal of the p-type transistor (M.sub.2) to ground at the time of the oscillation stop and disconnect a ground terminal and the gate terminal of the p-type transistor (M.sub.2) at the time of the oscillation operation. It is possible to implement low power consumption and high-speed oscillation activation of the oscillation circuit.

A constant-g.sub.m current source, arranged to generate a supply current for a Pierce oscillator. First and second transistors have source terminals connected to first and second supply rails, respectively, and drain terminals connected together and to the gate terminal of the first transistor. Third and fourth transistors have source terminals connected to the first and second supply rails, respectively, and drain terminals are connected together and to the gate terminal of the fourth transistor. An output portion varies the supply current in response to a voltage at the drain terminals of the third and fourth transistors. The gate terminals of the first and third transistors are connected together, and the gate terminals of the second and fourth transistors are connected together. An auto-calibration transistor has its source terminal connected to the first supply rail and its drain terminal connected to the source terminal of the first transistor.

A voltage controlled oscillator includes a resonator and an amplifier. The resonator includes a capacitive element and an inductive element. The inductive element has a plurality of conductive segments forming a physical loop. The inductive element has electrical connections on the physical loop to the plurality of conductive segments forming at least one electrical loop disposed within an interior space formed by the physical loop. The amplifier has an input and an output, the input coupled to a first conductive segment forming a first impedance and the output coupled to a second conductive segment forming a second impedance.

An oscillator circuit comprises a crystal oscillator and an inverter. The input of the inverter is connected to the first terminal of the crystal oscillator and the output of the inverter is connected to the second terminal of the crystal oscillator, oscillator circuit is arranged to operate the inverter in its linear operating region. An amplitude regulator has an input connected to the input of the inverter, arranged to provide a first supply current I.sub.AREG to the inverter, where the magnitude of the first supply current is inversely dependent on a magnitude of a voltage at the inverter input. A digital-to-analogue converter is arranged to provide a second supply current I.sub.DAC to the inverter having a magnitude determined by a digital signal applied to a digital input of the digital-to-analogue converter.

An oscillator circuit comprises a crystal oscillator arranged to generate an oscillation signal, a bias current generator arranged to supply a bias current to the crystal oscillator, and a feedback stage arranged to generate a feedback signal in response to an amplitude of the oscillation signal reaching an amplitude threshold. The bias current generator is arranged to: in response to a supply of power to the oscillator circuit being switched on, generate the bias current at an increasing level commencing from a first level; in response to the feedback signal, terminate the increasing; and during subsequent oscillation of the crystal oscillator, supply the bias current at a second level dependent on a final level of the bias current reached when the increasing is terminated.